Query

The Query operation finds items based on primary key values.
You can query any table or secondary index that has a composite primary key (a partition
key and a sort key).

Use the KeyConditionExpression parameter to provide a specific value
for the partition key. The Query operation will return all of the items
from the table or index with that partition key value. You can optionally narrow the
scope of the Query operation by specifying a sort key value and a
comparison operator in KeyConditionExpression. To further refine the Query results,
you can optionally provide a FilterExpression. A FilterExpression determines which items
within the results should be returned to you. All of the other results are discarded.

A Query operation always returns a result set. If no matching items are found,
the result set will be empty. Queries that do not return results consume the minimum
number of
read capacity units for that type of read operation.

Note

DynamoDB calculates the number of read capacity units consumed based on item size,
not on the amount of data that is returned to an application. The number of capacity
units consumed will be the same whether you request all of the attributes (the default
behavior)
or just some of them (using a projection expression). The number will also be the
same
whether or not you use a FilterExpression.

Query results are always sorted by the sort key value. If the data type of the sort key
is Number,
the results are returned in numeric order; otherwise, the results are returned in
order of UTF-8 bytes.
By default, the sort order is ascending. To reverse the order, set the ScanIndexForward parameter
to false.

A single Query operation will read up to the maximum number of items
set (if using the Limit parameter) or a maximum of 1 MB of data and then
apply any filtering to the results using FilterExpression. If
LastEvaluatedKey is present in the response, you will need to paginate
the result set. For more information, see Paginating
the Results in the Amazon DynamoDB Developer Guide.

FilterExpression is applied after a Query finishes, but before
the results are returned.
A FilterExpression cannot contain partition key or sort key attributes.
You need to specify those attributes in the KeyConditionExpression.

Note

A Query operation can return an empty result set and a LastEvaluatedKey
if all the items read for the page of results are filtered out.

You can query a table, a local secondary index, or a global secondary index. For a
query on a table or on a local secondary index, you can set the
ConsistentRead parameter to true and obtain a
strongly consistent result. Global secondary indexes support eventually consistent
reads
only, so do not specify ConsistentRead when querying a global
secondary index.

One or more substitution tokens for attribute names in an expression. The following
are some use cases for using ExpressionAttributeNames:

To access an attribute whose name conflicts with a DynamoDB reserved word.

To create a placeholder for repeating occurrences of an attribute name in an expression.

To prevent special characters in an attribute name from being misinterpreted in an
expression.

Use the # character in an expression to dereference an attribute name. For example, consider
the following attribute name:

Percentile

The name of this attribute conflicts with a reserved word, so it cannot be used directly
in an expression. (For the complete list of reserved words, see Reserved Words in the Amazon DynamoDB Developer Guide). To work around this, you could specify the following for
ExpressionAttributeNames:

{"#P":"Percentile"}

You could then use this substitution in an expression, as in this example:

#P = :val

Note

Tokens that begin with the : character are expression attribute values, which are placeholders for the actual value at runtime.

The condition that specifies the key value(s) for items to be retrieved by the Query
action.

The condition must perform an equality test on a single partition key value.

The condition can optionally perform one of several comparison tests on a single
sort key value. This allows Query to retrieve one item with a given
partition key value and sort key value, or several items that have the same partition
key value but different sort key values.

The partition key equality test is required, and must be specified in the following
format:

partitionKeyName=:partitionkeyval

If you also want to provide a condition for the sort key, it must be combined using
AND with the condition
for the sort key. Following is an example, using the = comparison operator for the sort key:

partitionKeyName=:partitionkeyvalANDsortKeyName=:sortkeyval

Valid comparisons for the sort key condition are as follows:

sortKeyName=:sortkeyval - true if the sort key value is equal to :sortkeyval.

sortKeyName<:sortkeyval - true if the sort key value is less than :sortkeyval.

sortKeyName<=:sortkeyval - true if the sort key value is less than or equal to
:sortkeyval.

sortKeyName>:sortkeyval - true if the sort key value is greater than :sortkeyval.

sortKeyName>= :sortkeyval - true if the sort key value is greater than
or equal to :sortkeyval.

sortKeyNameBETWEEN:sortkeyval1AND:sortkeyval2 - true if the sort key value is greater than or equal to
:sortkeyval1, and less than or equal to :sortkeyval2.

begins_with (sortKeyName, :sortkeyval) -
true if the sort key value begins with a particular operand. (You cannot use this
function with a sort key that is of type Number.) Note that the function name
begins_with is case-sensitive.

Use the ExpressionAttributeValues parameter to replace tokens such as
:partitionval and :sortval with actual values at runtime.

You can optionally use the ExpressionAttributeNames parameter to replace the names of
the partition key and sort key with placeholder tokens. This option might be necessary
if an attribute
name conflicts with a DynamoDB reserved word. For example, the following
KeyConditionExpression parameter causes an error because Size is a reserved
word:

Size = :myval

To work around this, define a placeholder (such a #S) to represent the attribute
name Size. KeyConditionExpression then is as follows:

#S = :myval

For a list of reserved words, see Reserved
Words in the Amazon DynamoDB Developer Guide.

The maximum number of items to evaluate (not necessarily the number of matching items).
If
DynamoDB processes the number of items up to the limit while processing the results,
it stops the
operation and returns the matching values up to that point, and a key in LastEvaluatedKey to
apply in
a subsequent operation, so that you can pick up where you left off. Also, if the processed
data set size
exceeds 1 MB before DynamoDB reaches this limit, it stops the operation and returns
the matching values
up to the limit, and a key in LastEvaluatedKey to apply in a subsequent operation to
continue the operation. For more information, see Query and Scan in the Amazon DynamoDB Developer Guide.

A string that identifies one or more attributes to retrieve from the table. These
attributes can include scalars, sets, or elements of a JSON document. The attributes
in the expression must be separated by commas.

If no attribute names are specified, then all attributes will be returned. If any
of the requested attributes are not found, they will not appear in the result.

Specifies the order for index traversal: If true (default), the traversal is performed in ascending order; if false, the traversal is performed in descending order.

Items with the same partition key value are stored in sorted order by sort key. If
the sort key data type is Number, the results are stored in numeric order. For type
String, the results are stored in order of UTF-8 bytes. For type Binary, DynamoDB
treats each byte of the binary data as unsigned.

If ScanIndexForward is true, DynamoDB returns the results in the order in which they are stored (by sort key
value). This is the default behavior. If ScanIndexForward is false, DynamoDB reads the results in reverse order by sort key value, and then returns
the results to the client.

The attributes to be returned in the
result. You can retrieve all item attributes, specific item attributes, the count
of
matching items, or in the case of an index, some or all of the attributes projected
into
the index.

ALL_ATTRIBUTES - Returns all of the item attributes from the
specified table or index. If you query a local secondary index, then for
each matching item in the index DynamoDB will fetch the entire item from the
parent table. If the index is configured to project all item attributes,
then all of the data can be obtained from the local secondary index, and no
fetching is required.

ALL_PROJECTED_ATTRIBUTES - Allowed only when querying an index.
Retrieves all attributes that have been projected into the index. If the
index is configured to project all attributes, this return value is
equivalent to specifying ALL_ATTRIBUTES.

COUNT - Returns the number of matching items, rather than the
matching items themselves.

SPECIFIC_ATTRIBUTES - Returns only the attributes listed in
AttributesToGet. This return value is equivalent to
specifying AttributesToGet without specifying any value
for Select.

If you query or scan a local secondary index and request only
attributes that are projected into that index, the operation will read only
the index and not the table. If any of the requested attributes are not
projected into the local secondary index, DynamoDB will fetch each of these
attributes from the parent table. This extra fetching incurs additional
throughput cost and latency.

If you query or scan a global secondary index, you can only request
attributes that are projected into the index. Global secondary index queries
cannot fetch attributes from the parent table.

If neither Select nor AttributesToGet
are specified, DynamoDB defaults to ALL_ATTRIBUTES when accessing a
table, and ALL_PROJECTED_ATTRIBUTES when accessing an index. You cannot
use both Select and AttributesToGet
together in a single request, unless the value for Select is
SPECIFIC_ATTRIBUTES. (This usage is equivalent to specifying
AttributesToGet without any value for
Select.)

Note

If you use the ProjectionExpression parameter, then
the value for Select can only be
SPECIFIC_ATTRIBUTES. Any other value for
Select will return an error.

Response Elements

The capacity units consumed by the Query operation. The data returned includes the total
provisioned throughput consumed, along with statistics for the table and any indexes
involved
in the operation. ConsumedCapacity is only returned if the ReturnConsumedCapacity parameter was specified
For more information, see Provisioned
Throughput in the Amazon DynamoDB Developer Guide.

The primary key of the item where the operation stopped, inclusive of the previous
result set. Use this value to start a new operation, excluding this value in the new
request.

If LastEvaluatedKey is empty, then the "last page" of results has been processed and there is no more
data to be retrieved.

If LastEvaluatedKey is not empty, it does not necessarily mean that there is more data in the result
set. The only way to know when you have reached the end of the result set is when
LastEvaluatedKey is empty.

The number of items evaluated, before any QueryFilter is applied. A high
ScannedCount value with few, or no, Count results indicates an inefficient
Query operation. For more information, see Count and ScannedCount in the
Amazon DynamoDB Developer Guide.

If you did not use a filter in the request, then ScannedCount is the same as
Count.

Type: Integer

Errors

For information about the errors that are common to all actions, see Common Errors.

InternalServerError

An error occurred on the server side.

HTTP Status Code: 500

ProvisionedThroughputExceededException

Your request rate is too high. The AWS SDKs for DynamoDB automatically retry requests
that
receive this exception. Your request is eventually successful, unless your retry queue
is too
large to finish. Reduce the frequency of requests and use exponential backoff. For
more
information, go to Error Retries and Exponential
Backoff in the Amazon DynamoDB Developer Guide.

HTTP Status Code: 400

ResourceNotFoundException

The operation tried to access a nonexistent table or index. The resource might not
be specified
correctly, or its status might not be ACTIVE.

HTTP Status Code: 400

Examples

Retrieve a Range of Items

The following example queries the Reply table for
replies in a forum that were posted by particular users. There is a local
secondary index on the Reply table,
PostedBy-Index, to facilitate fast lookups on the these
attributes.

The ProjectionExpression parameter determines which
attributes are returned.